A federal court has struck down rules that would have required libraries to block children's access to offensive Web material or lose federal funds, handing a win to librarians and free-speech advocates.

In a ruling Friday that blasted Web filtering technology for blocking both too much and too little on the Internet, a panel of the U.S. District Court for the Eastern District of Pennsylvania said that portions of the Children's Internet Protection Act (CIPA) violated the First Amendment and urged libraries to adopt other means to protect children from inappropriate material.

"Filtering products are currently unable to block only visual depictions that are obscene, child pornography, or harmful to minors (or only content matching a filtering product's category definitions) while simultaneously allowing access to all protected speech (or all content not matching the blocking product's category definitions)," the judges wrote. "Any software filter that is reasonably effective in blocking access to Web pages that fall within its category definitions will necessarily erroneously block a substantial number of Web pages that do not fall within its category definitions."

Congress passed the law in 2000, prompting groups such as the American Civil Liberties Union (ACLU) and the American Library Association (ALA) to sue to overturn it on free-speech grounds.

Friday's ruling cited multiple examples of the products' tendencies to overblock--one of the main arguments by opponents of the bill. The court noted that Web filters had erroneously labeled as adult or sexually explicit sites including those of orphanages, political candidates and churches.

"Although software filters provide a relatively cheap and effective, albeit imperfect, means for public libraries to prevent patrons from accessing speech that falls within the filters' category definitions, we find that commercially available filtering programs erroneously block a huge amount of speech that is protected by the First Amendment," the judges wrote.

Filtering companies scrambled to defend themselves after the ruling.

David Burt, a spokesman for filter software maker N2H2, said he was surprised by the tone of the ruling. "I thought they would come down with something a little more moderate than that," he said.

Burt compared a filtering company's efforts with those of the antivirus community, saying that the software companies have to rush to keep up with the constantly changing Web.

"We're never going to be 100 percent, and it seems like the court expects us to be 100 percent," he said.

Burt said library clients contribute to about 2 percent of the company's revenue, and he expects that many will continue to use filters on certain machines in spite of the ruling.

A community decision
Not surprisingly, librarians praised the decision.

"We are ecstatic that libraries can continue to serve our public and give them the information they need," said Carrie Gardner, chairwoman of the ALA's intellectual freedom roundtable.

Gardner said the ruling won't lead to immediate changes in libraries. She said some libraries already offer a filtering option on some machines, and she doubts they will stop doing that.

"A lot of libraries came to the decision to filter after having a dialogue with their communities," she said. "I don't know of anyone who's willing to push that aside."

Friday's ruling means libraries won't have to put filters on every machines.

Although the judges noted that some young people use libraries to access porn, they pointed out that the filters will not necessarily block out all material inappropriate for minors.

"Those public libraries that have responded to these problems by using software filters have found such filters to provide a relatively effective means of preventing patrons from accessing sexually explicit material on the Internet. Nonetheless, out of the entire universe of speech on the Internet falling within the filtering products' category definitions, the filters will incorrectly fail to block a substantial amount of speech," they wrote.

The judges suggested other methods of dealing with the problem than relying solely on filters. These methods include letting minors use unfiltered machines when accompanied by parents and putting terminals out of view of most patrons so they wouldn't be offended by material on the screen.

"While none of these less restrictive alternatives are perfect, the government has failed to show that they are significantly less effective than filtering software, which itself fails to block access to large amounts of speech that fall within the categories sought to be blocked," the judges wrote.

When it was passed, CIPA marked the latest in a long line of attempts by lawmakers to crack down on Web content. Courts also have overturned parts of earlier laws--including the Communications Decency Act--saying they violated free speech. Another law, the Child Online Protection Act, is still moving through the courts after a challenge by the ACLU.

Any appeal to Friday's ruling would automatically go to the U.S. Supreme Court.